Prior art closures for fluid containers are myriad in design and construction. These often require complicated molding, assembly of parts, are expensive to manufacture, do not close and seal properly, do not provide a variable closure opening dependent on the hand pressure used to dispense, are subject to opening upon inadvertent squeezing, and/or are of a shape not conducive to easy handling and shipping.
Prior art U.S. Pat. No. 1,977,227 (1934) discloses a closure wherein panels are separately placed in a mold in an overall frusto-conical shape, with rubber then poured over and under the panels to form a resilient part between the panels. An opening slit is then cut in the rubber. The frusto-conical shape of the panels is the closed position of the closure, and the panels cannot be folded to a flat position for ease of handling and shipping. Accordingly, the rubber is not folded in either the open or closed positions of the closure, and the sides of the panels are always separated. This multi-piece closure among other deficiencies is labor intensive and expensive to manufacture.
A further prior art closure is shown in PCT International Publication Number WO 82/01360 (1982), having a complex arrangement of triangular panels in overlapping layers of inner and outer seals, or a single layer of such panels but without interconnecting webs or membranes or other sealing means between the panels. In the latter instance, reliable sealing is unlikely, and opening upon inadvertent squeezing is not prevented.
Other prior art closures are known that have slitted configurations or various other constructions.